Computed Tomography Health Article

Preparation

If a contrast medium is administered, the patient may be asked to fast for about four to six hours prior to the procedure. Patients will usually be given a gown (like a typical hospital gown) to be worn during the procedure. All metal and jewelry should be removed to avoid artifacts on the film. Depending on the type of study, patients may also be required to remove dentures.

Aftercare

Generally, no aftercare is required following a CT scan. Immediately following the exam, the technologist will continue to watch the patient for possible adverse contrast reactions. Patients are instructed to advise the technologist of any symptoms, particularly respiratory difficulty. The site of contrast injection will be bandaged and may feel tender following the exam.

Risks

Radiation exposure from a CT scan is similar to, though higher than, that of a conventional x ray. Although this is a risk to pregnant women, the risk for other adults is minimal and should produce no effects. Severe contrast reactions are rare, but they are a risk of many CT procedures.

Normal results

Normal findings on a CT exam show bone, the most dense tissue, as white areas. Tissues and fat will show as various shades of gray, and fluids will be gray or black. Air will also look black. Intravenous, oral, and rectal contrast appear as white areas. The radiologist can determine if tissues and organs appear normal by the sensitivity of the gray shadows.

Abnormal results

Abnormal results may show different characteristics of tissues within organs. Accumulations of blood or other fluids where they do not belong may be detected. Radiologists can differentiate among types of tumors throughout the body by viewing details of their makeup.

Sinus studies

The increasing availability and lowered cost of CT scanning has lead to its increased use in sinus studies, either as a replacement for a sinus x ray or as a follow-up to an abnormal sinus radiograph. The sensitivity of CT allows for the location of areas of sinus infection, particularly chronic infection. Sinus tumors will show as shades of gray indicating the difference in their density from that of normal tissues in the area.

Brain studies

The precise differences in density allowed by CT scan can clearly show tumors, strokes, or lesions in the brain area as altered densities. These lighter or darker areas on the image may indicate a tumor or hematoma within the brain and skull area. Different types of tumors can be identified by the presence of edema, by the tissue's density, or by studying blood vessel location and activity. The speed and convenience of CT often allows for detection of hemorrhage before symptoms even occur.

Body scans

The body CT scan can identify abnormal body structures and organs. A CT scan may indicate tumors or cysts, enlarged lymph nodes, abnormal collections of fluids, blood or fat, or cancer metastasis. Tumors resulting from metastasis are different in makeup than primary (original) tumors.

Chest scans

In addition to those findings which may indicate aortic aneurysms, chest CT studies can show other problems in the heart and lungs, and distinguish between an aortic aneurysm and a tumor adjacent to the aorta. CT will not only show differences between air, water, tissues and bone, but will also assign numerical values to the various densities. Coin-sized lesions in the lungs may be indicative of tuberculosis or tumors. CT will help distinguish among the two. Enlarged lymph nodes in the chest area may indicate Hodgkin's disease.

Teresa G. Norris

Resources

BOOKS

Abeloff, M. Clinical Oncology, 2nd Ed. Orlando, Florida:Churchill Livingstone, Inc., 2000.

Springhouse Corporation. Illustrated Guide to Diagnostic Tests. Springhouse, PA: Springhouse Corporation, 1998.

PERIODICALS

Holbert, J. M. "Role of Spiral Computed Tomography in the Diagnosis of Pulmonary Embolism in the Emergency Department." Annals of Emergency Medicine (May 1999): 520-28.

ORGANIZATION

American College of Radiology. 1891 Preston White Drive, Reston, VA 22091. (800) ACR-LINE. <http://www.acr.org>.

Aneurysm

—The bulging of the blood vessel wall. Aortic aneurysms are the most dangerous. Aneurysms can break and cause bleeding.

Contrast (agent, medium)

—A substance injected into the body that illuminates certain structures that would otherwise be hard to see on the radiograph (film).

Gantry

—A name for the couch or table used in a CT scan. The patient lies on the gantry while it slides into the x-ray scanner.

Hematoma

—A collection of blood that has escaped from the vessels. It may clot and harden, causing pain to the patient.

Metastasis

—Secondary cancer, or cancer that has spread from one body organ or tissue to another.

Radiologist

—A medical doctor specially trained in radiology (x ray) interpretation and its use in the diagnosis of disease and injury.

Spiral CT

—Also referred to as helical CT, this method allows for continuous 360-degree x-ray image capture.